The research of solar cells is an anticipated direction for renewable energy sources. During the power generating process of solar cells, no greenhouse gas or pollutant gas, such as carbon diode, nitrogen oxides, and sulfur oxides, will be generated. Instead, the photoelectric effect is applied for converting solar energy into electric energy directly, endowing solar cells with technical advantages of not consuming nonrenewable resources. In the 21st century of running-out resources and rising prices of energy sources, solar cells are valued substantially.
Nonetheless, how to make solar energy a stable and sustainable energy source for humans is still a challenge. For current power generating technology using solar energy, there still exist many places for improvement, including stability, lifetime, or costs.
Among the types of solar cells, silicon solar cells are developed earlier and their energy conversion efficiency is higher. They can be further divided into single-crystalline and polycrystalline types. Generally, silicon solar cells adopt p-type silicon with impurity doping as the substrate. Then an n-type region layer is fabricated on its surface for forming p-n junctions.
The mainstream of producing front-grid electrode of silicon solar cells is through screen printing silvers; however, the ITRPV roadmap predicted that silver electrode would replaced by copper plated electrode since the cost of former is high. The Ni/Cu electrode is attractive; here, the main function of the nickel is used as a buffer layer between the silicon substrate and the copper, which prevents the decreasing of lifetime of solar cell by stopping the copper diffuses to the silicon substrate. At the same time, there is low specific contact resistance nickel where the nickel contacts the silicon substrate. However, Ni/Cu electrode is still not gain favor by industry. The reason is that the process of patternization of front-grid electrode is complicated. That is, the cost of material is lower, but the cost of process is becoming higher, thus the replacement of copper electrode still has barriers existed.
There are many methods for the patternization of plated metal electrodes in the present process. For example, in the laser ablation method, an antireflection layer is first coated on the silicon crystal. Then laser rays are used for bombarding the surface of the antireflection layer to vaporize the surface material of the antireflection layer and form voids. Next, electroless plating or light-induced plating (LIP) is used for forming metal electrodes in the voids of the antireflection layer.
In addition, screen-printing can be adopted. First, screen-print a metal thin layer made of patternized specific material, such as a thin silver film, on the surface of a formed antireflection layer. Afterwards, metal electrodes are formed on the silver film via LIP.
Moreover, the technology of laser firing can be used. A metal layer, such as a nickel layer, is first plated on the surface of silicon crystals. Then laser rays are used for firing specific patterns and forming nickel silicides on the fired spots of the nickel layer. Next, acid liquid is used to remove the nickel metal while keeping the portion of the formed nickel silicides.